The present application relates to semiconductor device manufacturing, and in particular, to automatically controlling metal thickness during film deposition using X-ray fluorescence (XRF) detection.
During semiconductor device manufacturing, thin metal layers are deposited on semiconductor wafers to form vias, lines and various layers such as diffusion barriers, adhesion or seed layers, primary conductors, antireflection coatings, and etch stops. For example, sputter deposition, also known as physical vapor deposition (PVD), is widely used for the fabrication of metal thin-film structures on semiconductor wafers. Sputtering involves removing atoms from a solid material and then depositing the resultant vapor on a nearby substrate.
Sputter deposition is usually carried out in diode plasma systems known as magnetrons, in which the cathode is sputtered by ion bombardment and emits the atoms, which are then deposited on the wafer in the form of a thin film. Depending on the lithography scheme, these films are then etched by means of reactive ion etching (RIE) or polished using chemical-mechanical polishing (CMP) to help delineate circuit features.
The principal type of system currently used for high-rate deposition of metals, alloys, and compounds is known as the magnetron cathode system. This type of tool uses magnetic confinement of electrons in the plasma, which results in a higher plasma density than in either radio-frequency (rf) or direct-current (dc) diode systems. The higher plasma density reduces the discharge impedance and results in a much higher-current, lower-voltage discharge. As a rough example, an rf diode tool operating at 2 kW might have a peak-to-peak rf voltage of over 2000 V. A conventional magnetron system operated at 2 kW might have a dc discharge voltage of 400 V and an ion current of 5 A to the cathode.
Current manufacturing-scale magnetron systems are constructed from stainless steel. They are typically configured with cryopumps connected directly to their deposition chambers by means of large-diameter valves, and the resultant base pressure is generally in the low 10xe2x88x928-Torr range for most cathodes, and in the 10xe2x88x929-Torr range for Ti, for which the chemically active nature of the deposited films can contribute appreciably to the net pumping speed of the system.
The working pressure during sputtering is typically 0.5 to 30 mTorr, which requires a gas flow of many tens of standard cubic centimeters per minute (sccm). Because of base-pressure considerations, manufacturing-level systems are not baffled and therefore retain approximately the true base pressure of the chamber during deposition. The magnetron chambers used for large-scale semiconductor applications are configured as ports on an integrated-process load-locked tool, and wafers are introduced to the deposition chamber via a load lock
Sputter deposition is managed by deposition time. The rate is calibrated against time, and then films are deposited for a fixed time period. However, due to process variations, thickness of deposited films for specific wafers or lots is hard to control during film deposition. Typically, metal film thickness is measured after deposition on some sampled wafers.
However, mechanical and electrical properties of fabricated semiconductor devices strongly depend on metal film thickness. Thickness variations greatly affect the device performance. Therefore, it would be desirable to control metal film thickness on every wafer during film deposition.
The present invention offers a novel method of monitoring a parameter of a metal film being deposited on a wafer during semiconductor device fabrication. The method involves producing an X-ray beam directed to a metal film during deposition of the metal film on the wafer in a deposition chamber, and detecting the X-ray fluorescence of the metal film to determine the required parameter of the film.
The determined parameter may be compared with a preset value to continue deposition of the metal film if the determined parameter differs from the preset value. Deposition of the metal film may be stopped when the determined parameter coincides with the preset value.
In accordance with one aspect of the present invention, thickness of a metal film being deposited on a wafer is automatically controlled during film deposition by producing an X-ray beam directed to the metal film, and detecting X-ray fluorescence of the film.
The thickness of the metal film determined based on the detected X-ray fluorescence may be compared with a preset value to continue deposition if the determined thickness is less than the preset value. Deposition may be stopped when the determined thickness reaches the preset value.
Still other aspects and advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein only the preferred embodiment of the invention is shown and described, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.